Last change
on this file since 577 was
444,
checked in by satin@…, 6 years ago
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add newlib,libalmos-mkh, restructure shared_syscalls.h and mini-libc
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File size:
881 bytes
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Line | |
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1 | #include <stdlib.h> |
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2 | |
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3 | /* Pseudo-random generator based on Minimal Standard by |
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4 | Lewis, Goodman, and Miller in 1969. |
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5 | |
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6 | I[j+1] = a*I[j] (mod m) |
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7 | |
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8 | where a = 16807 |
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9 | m = 2147483647 |
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10 | |
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11 | Using Schrage's algorithm, a*I[j] (mod m) can be rewritten as: |
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12 | |
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13 | a*(I[j] mod q) - r*{I[j]/q} if >= 0 |
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14 | a*(I[j] mod q) - r*{I[j]/q} + m otherwise |
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15 | |
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16 | where: {} denotes integer division |
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17 | q = {m/a} = 127773 |
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18 | r = m (mod a) = 2836 |
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19 | |
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20 | note that the seed value of 0 cannot be used in the calculation as |
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21 | it results in 0 itself |
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22 | */ |
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23 | |
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24 | int |
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25 | rand_r (unsigned int *seed) |
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26 | { |
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27 | long k; |
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28 | long s = (long)(*seed); |
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29 | if (s == 0) |
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30 | s = 0x12345987; |
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31 | k = s / 127773; |
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32 | s = 16807 * (s - k * 127773) - 2836 * k; |
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33 | if (s < 0) |
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34 | s += 2147483647; |
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35 | (*seed) = (unsigned int)s; |
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36 | return (int)(s & RAND_MAX); |
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37 | } |
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